The metal casting industry cannot be separated from the occurrence of product defects. Because of this, the quality of the products produced will decrease and will cause the company's funds to be greater. Four types of defects occur in the product, including porous defects, cohesive defects, incomplete defects, and deformation defects. The purpose of this research is to find out the causes of the defects that occur and find out what prevention can be done to reduce the number of funds used but still produce quality products. The production data showed that the cohesive defects were the most common defects, then observations and analyses were carried out. From the results of the analysis, the causes of defects are divided into two factors, namely general factors such as human error and special factors such as errors that occur during the casting process. Prevention efforts that can be done are conducting job training, conducting performance appraisals, and increasing supervision of worker activities.